JP2023083302A - Cleaning surface of optic located in chamber of extreme ultraviolet light source - Google Patents

Abstract

To provide systems and methods for cleaning a surface of an optic located in a chamber of an extreme ultraviolet light source.SOLUTION: Described is a method of cleaning a surface of an optic (115) within a chamber (125) of an extreme ultraviolet (EUV) light source (100). The chamber is held at a pressure below atmospheric pressure. The method includes generating a material in a plasma state at a location adjacent to an optical surface (110) and within the chamber, the generating step comprising transforming a native material (135) that is already present within the vacuum chamber and adjacently to the optical surface from a first state into the plasma state (130). The plasma state of the material includes free radicals of the material. The material in the plasma state is generated by enabling the material in the plasma state to move to the entire optical surface to remove debris (107) from the optical surface without removing the optic from the EUV light source.SELECTED DRAWING: Figure 1

Description

(Cross reference to related applications)
[0001] This application claims priority to US Application No. 62/580,827, filed November 2, 2017. which is hereby incorporated by reference in its entirety.

[0002] The disclosed subject matter relates to systems and methods for cleaning surfaces of optics within a chamber of an extreme ultraviolet light source.

[0003] For example, extreme ultraviolet (EUV) light, such as electromagnetic radiation having wavelengths of about 50 nm or less (sometimes referred to as soft x-rays) and including light at wavelengths of about 13 nm, is used in photolithographic processes. It can be used, for example, to produce very small features in substrates such as silicon wafers.

[0004] Methods of producing EUV light include, but are not necessarily limited to, converting materials having elements with emission lines in the EUV range, such as xenon, lithium, or tin, into a plasma state. In one such method, often referred to as laser produced plasma ("LPP"), a target material, e.g., in the form of droplets, plates, tapes, streams, or clusters of material, is irradiated with an amplified light beam. By doing so, the required plasma can be generated. For this process, the plasma is typically generated in a closed container, such as a vacuum chamber, and monitored using various types of metrology equipment.

[0005] In some general aspects, a method is used for cleaning surfaces of optics within a chamber of an extreme ultraviolet (EUV) light source. The chamber is held at a pressure below atmospheric pressure. The method includes generating material in a plasma state at a location within the chamber adjacent to the optical surface. Generating includes converting a native material already present in the vacuum chamber adjacent the optical surface from a first state to a plasma state. The plasma state of the material contains free radicals of the material. To generate the material in the plasma state, at least the material in the plasma state is moved over the optical surface to allow removal of debris from the optical surface without removing the optics from the EUV light source.

[0006] Implementations may include one or more of the following features. For example, material in a plasma state can be generated by electromagnetically inducing a current at a location in the chamber adjacent to the optical surface. A current in the chamber adjacent to the optical surface can be induced by generating a time-varying magnetic field in the vicinity of the optical system in the chamber. A time-varying magnetic field within the chamber can be generated by passing a time-varying current through an electrical conductor positioned outside the perimeter of the optical surface.

[0007] The material in the plasma state can move across the optical surface to remove debris from the optical surface without the presence of oxygen.

[0008] The material in the plasma state may include at least hydrogen ions, electrons, and free radicals.

[0009] Debris can be removed by chemically reacting free radicals of the material with the debris on the optical surface to form chemicals that are released from the optical surface. The method may also include removing released chemicals from the EUV chamber. The free radicals are hydrogen free radicals and the debris on the photosurface may contain tin, such that the chemicals released from the photosurface include tin hydride.

[00010] Debris can be removed from the optical surface by etching the debris from the optical surface at a rate of at least 1 nanometer/minute over the entire optical surface.

[00011] In another general aspect, a system includes an extreme ultraviolet (EUV) light source and a cleaning device. The EUV light source comprises an EUV chamber maintained at subatmospheric pressure and a target delivery system that directs the target toward an interaction region within the vacuum chamber, the interaction region receiving an amplified light beam; The target includes a target delivery system including a material that emits extreme ultraviolet light when converted to plasma, and a light collector including a surface that interacts with at least a portion of the emitted extreme ultraviolet light. A cleaning device is adjacent to the light collector surface and configured to remove debris from the light collector surface without removing the collector from the EUV chamber. The cleaning apparatus includes a plasma generator within the EUV chamber adjacent to the light collector surface. A plasma generator generates plasma material in a plasma state adjacent to the light collector surface from native material already existing in a first state in the EUV chamber adjacent to the light collector surface. The plasma material contains free radicals that chemically react with debris on the light collector surface.

[00012] Implementations can include one or more of the following features. For example, the surface of the light collector is a reflective surface and the interaction of the emitted extreme ultraviolet light with the light collector surface can include reflection of the emitted extreme ultraviolet light from the light collector surface.

[00013] The plasma generator may include an electrical conductor positioned adjacent to the light collector surface. The conductor is connected to a power supply. A power source produces a time-varying magnetic field adjacent to the light collector surface by supplying a time-varying current through the electrical conductor and induces a current at a location adjacent to the light collector surface. The induced current may be sufficiently large to generate material in a plasma state adjacent to the light collector surface from native material already present in the EUV chamber in a first state. The conductor may be shaped to match the shape of the light collector surface. The plasma generator may include a dielectric material that at least partially surrounds the conductor. The dielectric material may include tubing surrounding at least a portion of the conductor. The tube may be in contact with a portion of the conductor.

[00014] The conductor may be shaped to match the shape of the rim at the edge of the light collector surface.

[00015] The light collector surface may be elliptical in shape and the conductor may comprise a circle having a diameter greater than the circumference of the light collector surface.

[00016] The native material already present in the chamber in a first state may comprise hydrogen, and the material in the plasma state may comprise at least hydrogen ions, electrons, and free radicals.

[00017] Chemical reactions between free radicals and debris on the light collector surface can form chemicals that are released from the light collector surface. The system can also include a removal device configured to remove chemicals released from the EUV chamber.

[00018] The cleaning apparatus may include an inductively-coupled (ICP) plasma source.

[00019] In another general aspect, a method is performed for cleaning surfaces of optics within a chamber of an extreme ultraviolet (EUV) light source. The chamber is held at a pressure below atmospheric pressure. The method includes generating material in a plasma state at a location within the chamber adjacent to the optical surface. Generating includes converting a material within the vacuum chamber from a first state to a plasma state by electromagnetically inducing a current at a location adjacent to the optical surface within the chamber. The plasma state of the material contains free radicals of the material. To generate the material in the plasma state, at least the material in the plasma state is moved over the optical surface to allow removal of debris from the optical surface without removing the optics from the EUV light source.

[0020] Implementations can include one or more of the following features. For example, the material can be in the first state and adjacent to the optical surface before being transformed.

[0021] A current at a location adjacent to the optical surface within the chamber can be induced by generating a time-varying magnetic field near an optical system within the chamber. A time-varying magnetic field within the chamber can be generated by passing a time-varying current through an electrical conductor positioned outside the perimeter of the optical surface.

[0022] The material in the plasma state is capable of moving across the optical surface and removing debris from the optical surface without the presence of oxygen.

[0023] The material in the plasma state may include at least hydrogen ions, electrons, and free radicals.

[0024] Debris can be removed from an optical surface by chemically reacting free radicals of the material with the debris on the optical surface to form chemicals that are released from the optical surface. The method may also include removing released chemicals from the EUV chamber. The free radicals are hydrogen free radicals and the debris on the photosurface may contain tin, such that the chemicals released from the photosurface include tin hydride.

[0025] Materials in the vacuum chamber can be native and present in the vacuum chamber.

[0026] The disclosed cleaning apparatus and methods allow the ICP plasma source to be placed in a vacuum, minimizing or reducing the need to modify the EUV chamber. Because the ICP plasma source design is not placed in the atmosphere during operation, there is no need to transport the plasma or free radicals into the EUV chamber, which reduces the complexity of the ICP plasma sources described herein. In some implementations, the ICP plasma source operates within the vacuum environment of the EUV chamber by being fabricated with a segmented bead of dielectric material such as porcelain, ceramic, mica, polyethylene, glass, or quartz. is designed to Such a design reduces the risk of air leaks due to failure of the ICP plasma source. The disclosed cleaning apparatus and methods remove debris such as tin from optical surfaces at least 10 times faster, or at least 100 times faster than conventional techniques such as filament cleaning (HRG) and microwave cleaning systems (etching, etc.). ).

[00027] Fig. 3 is a block diagram of a cleaning apparatus for removing debris from the surfaces of optics within an extreme ultraviolet (EUV) light source; [00028] Fig. 2 is a block diagram of an exemplary EUV light source, wherein the cleaning device is designed as an inductively coupled plasma (ICP) cleaning device; [00029] Fig. 3 is a first side perspective view of a collector mirror that can be cleaned using the cleaning apparatus of Fig. 1 or 2; [00030] FIG. 3B is a second side perspective view of the collector mirror of FIG. 3A; [00031] FIG. 3B is a cross-sectional side view of the collector mirror of FIG. 3A. [00032] FIG. 3B is a plan view along a second side of the collector mirror of FIG. 3B; [00033] Figure 3 is a perspective view of an ICP cleaning apparatus that can be used in the EUV light source of Figure 1 or Figure 2; [00034] FIG. 4B is a cross-sectional side view along plane BB of the ICP cleaning arrangement of FIG. 4A. [00035] FIG. 4C is a side cross-sectional view of section C of the ICP cleaning apparatus of FIG. 4B. [00036] Fig. 4C is a plan view of the ICP cleaning apparatus of Figs. 4A-4C; [00037] Fig. 3 is a perspective view of an ICP cleaning apparatus that can be used in the EUV light source of Fig. 1 or 2; [00038] FIG. 5B is a cross-sectional side view along plane BB of the ICP cleaning arrangement of FIG. 5A. [00039] FIG. 5B is a cross-sectional side view of section C of the ICP cleaning apparatus of FIG. 5B. [00040] Fig. 5C is a plan view of the ICP cleaning apparatus of Figs. 5A-5C; [00041] Fig. 5D is a plan view of section E of the ICP cleaning apparatus of Fig. 5D. [00042] Fig. 3 is a plan view of an ICP cleaning apparatus that can be used in the EUV light source of Fig. 1 or 2; [00043] FIG. 6B is a perspective view of the ICP cleaning arrangement of FIG. 6A. [00044] FIG. 6B is a plan view of section C of the ICP cleaning apparatus of FIG. 6A. [00045] Fig. 3 is a flow chart of a procedure for cleaning the surface of an optical system using the cleaning apparatus of Figures 1 and 2; [00046] Fig. 8 is a schematic diagram showing the steps of the procedure of Fig. 7; [00047] Fig. 8 is a schematic diagram illustrating the steps of the procedure of Fig. 7; [00048] Fig. 6 is a flowchart of a procedure for converting material in an EUV chamber from a first state to a plasma state; [00049] Fig. 3 is a graph of removal rate versus distance by the cleaning apparatus of Figures 1 and 2 as compared to conventional cleaning techniques, the vertical axis being a linear scale; [00050] Fig. 3 is a graph of removal rate versus distance by the cleaning apparatus of Figures 1 and 2 as compared to conventional cleaning techniques, the vertical axis being a non-linear scale; [00051] Figure 3 depicts a block diagram of a lithographic apparatus that receives the output of the EUV light source of Figure 2; [00052] Figure 3 depicts a block diagram of a lithographic apparatus that receives the output of the EUV light source of Figure 2;

[00053] Referring to FIG. The optics 115 are housed within the cavity of an EUV chamber 125 which is held at vacuum or sub-atmospheric pressure. The cleaning apparatus 105 includes a plasma generator 180 that generates material in a plasma state (plasma material 135 ) from the native material already present in the EUV chamber 125 (native material 135 ) at a location local to or adjacent to the optical surface 110 . 130) can be generated or generated. A material 135 is native or present within the EUV chamber 125 if it is present within the EUV chamber 125 without having to be transported into the EUV chamber 125 from outside the EUV chamber 125 . Plasma material 130 chemically reacts with debris 107 , thereby dislodging debris 107 from optical surface 110 and forming new chemicals 137 that can be removed from EUV chamber 125 . The new chemical 137 may be in a gaseous state such that it is released from the optical surface 110 as it is formed. Removal from the EUV chamber 125 involves pumping new chemicals 137 from the EUV chamber 125 .

[00054] The EUV light source 100 includes a target delivery system 140 that directs a flow 145 of targets 150 toward an interaction region 155 within the EUV chamber 125. As shown in FIG. Interaction region 155 receives amplified light beam 160 . Target 150 includes a material that emits EUV light when in a plasma state. The interaction of this material within target 150 with amplified light beam 160 in interaction region 155 transforms a portion of the material within target 150 into a plasma state. This converted material can be referred to as light emitting plasma 170 . Light emitting plasma 170 emits EUV light 165 . The light emitting plasma 170 has elements with emission lines in the EUV wavelength range. The light emitting plasma 170 produced has certain characteristics that depend on the composition of the target 150 . These features include the wavelength of EUV light 165 produced by light emitting plasma 170 .

[00055] For clarity, light emitting plasma 170 of target 150 differs from plasma material 130 in the following ways. Light emitting plasma 170 is generated by the interaction of target 150 and amplified light beam 160 . Furthermore, the light emitting plasma 170 of the target 150 is what produces the EUV light 165 . Plasma material 130 , on the other hand, is produced from native material 135 present inside chamber 125 . Neither native material 135 nor plasma material 130 contribute to the production of EUV light 165 . Moreover, plasma material 130 is not produced from the interaction of native material 135 with amplified light beam 160 .

[00056] The presence of the target 150 and the interaction of the target 150 with the amplified light beam 160 can generate debris 107 in the form of particles, vapor residues, or pieces of material present within the target 150. be. This debris may accumulate on surfaces of objects in the path of light emitting plasma 170 . For example, if the target 150 contains molten metal of tin, tin particles can accumulate on the light surface 110 . Accordingly, debris 107 formed on optical surface 110 may include vapor residues, ions, particles, and/or clusters of material formed from target 150 . The presence of debris 107 can reduce the performance of the optical surface 110 and further reduce the overall efficiency of the EUV light source 100 . Therefore, in order to improve the performance of the EUV light source 100, it is beneficial to clean the optical surface 110 with the cleaning device 105. FIG. The optical system 115 is located inside the EUV chamber 125 and removing the optical system 115 is time consuming for the operation of the EUV light source 100 . The disclosed cleaning apparatus 105 generates plasma material 130 locally at the optical surface 110 . Thus, there is no need to transport plasma material 130 from outside EUV chamber 125 to a location local to or adjacent optical surface 110 . Further, debris 107 can be removed from optical surface 110 without having to remove optical surface 110 and optics 115 from EUV chamber 125 . Because of its relative position, cleaning device 105 can remove debris 107 at a faster rate than previous cleaning techniques. Further, cleaning apparatus 105 can generate plasma material 130 without requiring the presence of oxygen in a vacuum environment.

[00057] Optics 115 may be a light collector whose surface 110 interacts with at least a portion of the emitted EUV light 165. FIG. For example, surface 110 of light collector 115 may be a reflective surface positioned to receive at least a portion of EUV light 165 and reflect this EUV light 175 for use outside EUV light source 100 . For example, EUV light 175 can be directed towards the lithographic apparatus. The reflective surface 110 can be configured to reflect light within the EUV wavelength range but absorb or diffuse or block light outside the EUV wavelength range.

The cleaning apparatus 105 includes a plasma generator 180 positioned adjacent to the optical surface 110 and entirely within the EUV chamber 125 . The cleaning apparatus 105 also includes a power supply 185 that powers the plasma generator 180 . A native material 135 already exists within the EUV chamber 125, at least a portion of which is adjacent to the optical surface 110 and in a first material state. Plasma generator 180 generates plasma material 130 from native material 135 at a location adjacent optical surface 110 . Plasma material 130 contains free radicals that chemically react with debris 107 on photosurface 110 . These free radicals are generated from native material 135 . Free radicals are atoms, molecules, or ions with unvalent electrons or vacant electron shells and are therefore thought to have dangling covalent bonds. Dangling bonds can make free radicals more chemically reactive. That is, free radicals can readily react with other substances. Because of this reactive nature, free radicals can be used to remove material (such as debris 107 ) from objects such as optical surface 110 . Free radicals in plasma material 130 may remove debris 107 by, for example, etching debris 107 , reacting with debris 107 , and/or burning debris 107 .

[00059] In addition to free radicals, plasma material 130 does not react with debris 107, such as ions formed from native material 135, electrons produced from native material 135, and chemically neutral items. Other ingredients may also be included. The more free radicals present in plasma material 130, the more debris 107 cleaning device 105 can remove. Stated another way, the higher the density of free radicals within the plasma material 130, the faster the debris removal rate.

[00060] In some implementations, the native material 135 is composed of molecular hydrogen in the gaseous state. The plasma generator 180 in these implementations generates a plasma material comprising hydrogen free radicals from hydrogen molecules. The plasma material may also include hydrogen ions, electrons, and hydrogen molecules.

[00061] As noted above, the cavity within the EUV chamber 125 is maintained at a vacuum or pressure below atmospheric pressure. For example, EUV chamber 125 may be held at a low pressure (eg, 1 T) between about 0.5 Torr (T) and about 1.5 T, which is the pressure selected for generating EUV light 165 . Cleaning apparatus 105 is configured to generate plasma material 130 within EUV chamber 125, which means that it is designed to work in a vacuum (such as 1 T). Further, cleaning device 105 is configured to act on native material 135, and in some implementations available native material 135 is molecular hydrogen. Cleaner 105 does not act on target 150 . Further, cleaning apparatus 105 is designed to be used without the need to change the design or operation of EUV chamber 125 . Cleaning apparatus 105 is thus configured to operate in an environment in which EUV light 165 is most efficiently produced.

[00062] As mentioned above, the target delivery system 140 directs the flow 145 of the targets 150 toward the interaction region 155 within the EUV chamber 125. FIG. Target delivery system 140 targets targets 150 in flow 145 in the form of liquid droplets, liquid streams, solid particles or clusters, solid particles contained in liquid droplets, or solid particles contained in liquid streams. Send, control and direct. Target 150 may be any material that emits EUV light when in a plasma state. For example, target 150 may include water, tin, lithium, and/or xenon. Target 150 may be a target mixture that includes target material and impurities such as non-target particles. A target material is a material that has emission lines in the EUV range when in the plasma state. The target material may be, for example, droplets of liquid or molten metal, part of a liquid stream, solid particles or clusters, solid particles contained in liquid droplets, bubbles of target material, or solids contained in part of a liquid stream. It can be particles. The target material may be, for example, water, tin, lithium, xenon, or any material that has emission lines in the EUV range when converted to the plasma state. For example, the target material can be a tin element, such as pure tin (Sn), tin compounds such as SnBr4, SnBr2, SnH4, such as tin-gallium alloys, tin-indium alloys, tin-indium-gallium alloys, or as a tin alloy such as any combination of these alloys. Further, in the absence of impurities, target 150 contains only target material.

[00063] Light-emitting plasma 170 is believed to be a highly ionized plasma having an electron temperature of tens of electron volts (eV). Higher energy EUV light 165 can also be generated by other fuel materials (other types of targets 150), such as terbium (Tb) and gadolinium (Gd). High-energy radiation generated during de-excitation and recombination of these ions is emitted from the plasma and then collected by optics 115 .

[00064] Some of the free radicals of the plasma material 130, after being formed in the plasma generator 180, flow through the light surface 110 by the action of diffusion. However, due to the relatively high pressure within the EUV chamber 125 (which may be a vacuum but not a high vacuum), it may be difficult for the free radicals of the plasma material 130 to disperse to the optical surface 110 without additional assistance. . Accordingly, cleaning apparatus 105 can also include a gas flow mechanism 184 configured to drive or disperse free radicals of plasma material 130 across the surface of optical surface 110 .

[00065] Referring to Figure 2, an exemplary EUV light source 200 is shown. In EUV light source 200 , cleaning device 105 is designed as an inductively coupled plasma (ICP) cleaning device 205 designed to clean debris 207 from reflective surface 210 of collector mirror 215 . Cleaning apparatus 205 includes a plasma generator 280 positioned adjacent reflective surface 210 and entirely within EUV chamber 225 . The cleaning apparatus 205 also includes a power supply 285 that powers the plasma generator 280 .

[00066] Similar to EUV light source 100, EUV light source 200 includes a target delivery system 240 that delivers a stream 245 of targets 250 toward interaction region 255 and an amplified light beam 260 that is directed toward interaction region 255. including. In interaction region 255 , the interaction of amplified light beam 260 with target 250 converts at least a portion of target 250 into a plasma state 270 that produces EUV light 265 . After describing the EUV light source 200, the cleaning apparatus 205 will be discussed. EUV light source 200 includes other components not shown in FIG. 2, such as, for example, components for monitoring aspects of the production of EUV light 265 or components for controlling aspects related to amplified light beam 260. obtain.

[00067] The EUV light source 200 includes an optical system 261 that produces an amplified light beam 260 by population inversion in one or more gain media. Optical system 261 may include a light source that produces a light beam and a beam delivery system that directs and alters the light beam and focuses the light beam onto interaction region 255 . A light source in optics 261 provides one or more main pulses that form an amplified light beam 260, and optionally also one or more pre-pulses that form a precursor amplified light beam (not shown). Contains one or more optical amplifiers, lasers, and/or lamps. Each optical amplifier includes a gain medium, a pump source, and internal optics capable of optically amplifying a desired wavelength with high gain. The optical amplifier may or may not have laser mirrors or other feedback devices that form the laser cavity. Thus, optical system 261 produces amplified light beam 260 due to population inversion in the gain medium of the amplifier, even in the absence of a laser cavity. Further, optical system 261 can produce amplified light beam 260 which is a coherent laser beam if a laser cavity is present that provides sufficient feedback to optical system 261 . Thus, the term "amplified light beam" refers to light from optical system 261 that is amplified but not necessarily coherent lasing, and light from optical system 261 that is amplified but not necessarily coherent lasing. includes one or more.

[00068] The optical amplifier used in optical system 261 includes a gas including carbon dioxide ( _CO2 ) as a gain medium, and emits light having a wavelength of about 9100 to about 11000 nanometers (nm), such as about 10600 nm, to 100 or more can be amplified by the grain of Amplifiers and lasers suitable for use in optical system 261 include pulsed laser devices. This is, for example, a pulsed gas discharge _CO2 laser device that produces radiation of about 9300 nm or about 10600 nm by DC or RF excitation and operates at relatively high powers, for example 10 kW or more, and high pulse repetition rates, for example 40 kHz or more.

[00069] In some implementations, the target 250 comprises tin (Sn), as discussed above, and in these implementations the debris 207 on the reflective surface 210 comprises tin particles. As discussed above, the EUV chamber 225 is a controlled environment and one of the permissible materials present in the EUV chamber 225 is molecular hydrogen (H ₂ ) 235 . In this case, cleaning device 205 produces plasma material 230 from molecular hydrogen 235 . This plasma material 230 contains hydrogen free radicals that interact with debris 207 (including tin particles) on the reflective surface 210 . A hydrogen free radical is a single hydrogen element (H*). This chemical process can be represented by the following chemical formula.

where g indicates that the chemical is in gaseous state.

[00070] Specifically, the generated hydrogen H* free radicals combine with tin particles (Sn) on the reflective surface 210 to form a new chemical 237 called tin hydride ( _SnH4 ). , which is released from the reflective surface 210 . This chemical process is represented by the following chemical formula.

where s indicates that the chemical is in solid state.

[00071] Debris 207 may be etched or removed from reflective surface 210 at a rate of at least 1 nanometer/minute over the entire reflective surface 210, not just the area closest to cleaning apparatus 205. This is because the plasma material 230 is generated adjacent to the reflective surface 210 rather than being generated outside the EUV chamber 225 and then transported into the EUV chamber 225 . This is important because the hydrogen radical H* is short-lived and tends to recombine to reform molecular hydrogen. The design of the cleaning device 205 allows the hydrogen radicals H* to form as close as possible to the reflective surface 210, thereby allowing the hydrogen radicals H* to form before they have a chance to recombine with each other and reform molecular hydrogen. More hydrogen radicals H* can bond with tin particles.

[00072] Referring also to FIGS. Collector mirror 215 includes a reflective surface 210 that interacts with EUV light 265 produced from the interaction of target 250 and amplified light beam 260 in interaction region 255 . Reflective surface 210 reflects EUV light 275 , which is at least a portion of EUV light 265 , to secondary focal plane 266 where EUV light 275 is reflected to tool 290 (such as a lithographic apparatus) external to EUV light source 200 . captured for use by After a detailed description of the EUV light sources 100, 200, exemplary lithographic apparatus 1190, 1290 will be discussed with reference to FIGS. 11 and 12. FIG. Collector mirror 215 may be, for example, an elliptical mirror having a primary focus at interaction region 255 and a secondary focus at secondary focal plane 266 . This means that the planar section (such as planar section CC) is elliptical or circular in shape. Planar section CC is thus transverse to reflective surface 210 and is formed from a portion of an ellipse. A plan view of collector mirror 215 shows that edge 211 of reflective surface 210 forms a circle.

[00073] Although the collector mirror 215 shown herein is a single curved mirror, the collector mirror 215 may take other forms. For example, collector mirror 215 may be a Schwarzschild collector with two radiation collecting surfaces. In one implementation, collector mirror 215 is a grazing-incidence collector that includes a plurality of mutually nested substantially cylindrical reflectors.

[00074] The EUV light source 200 also includes a controller 292 in communication with one or more controllable components or systems of the EUV light source 200. FIG. Controller 292 is in communication with optics 261 and target delivery system 240 . Target delivery system 240 may be operable in response to signals from one or more modules within controller 292 . For example, the controller 292 can send a signal to the target delivery system 240 to change the emission point of the target 250 to compensate for errors in reaching the desired interaction area 255 . Optical system 261 may be operable in response to signals from one or more modules within controller 292 . Controller 292 may include modules for controlling power supply 285 of cleaning device 205 . The various modules of controller 292 can be independent modules in that data between modules is not transferred from module to module. Alternatively, one or more of the modules within controller 292 may communicate with each other. The modules within controller 292 may be physically co-located or separate from each other. For example, the module that controls power supply 285 can be co-located with power supply 285 .

[00075] The EUV system 200 also includes a removal or evacuation device 295 configured to remove released chemicals 237 from the EUV chamber 225, as well as other gaseous byproducts that may be formed within the EUV chamber 225. Also includes Removal device 295 may be a pump that removes released chemicals 237 from EUV chamber 225 . For example, chemicals 237 are released as they are formed, but because chemicals 237 may be volatile, they are drawn into stripper 295 , which removes released chemicals 237 from EUV chamber 225 .

[00076] Other components of the EUV light source 200 that are not shown include, for example, a detector for measuring parameters associated with the EUV light 265 produced. A detector can be used to measure the energy or energy distribution of the amplified light beam 260 . A detector can be used to measure the angular distribution of the intensity of the EUV light 265 . The detector can measure pulse timing or focus errors in the amplified light beam 260 . Output from these detectors can be provided to controller 292 . Controller 292 may include modules that analyze this output and adjust aspects of other components of EUV light source 200 such as optics 261 and target delivery system 240 .

[00077] In summary, amplified light beam 260 is generated by optics 261 and directed along a beam path to irradiate target 250 at interaction region 255, thereby dissolving material within target 250 in the EUV wavelength range. Converts into a plasma that emits light within. Amplified light beam 260 operates at a particular wavelength (source wavelength) determined based on the design and characteristics of optical system 261 .

[00078] Referring to FIGS. 4A-4D, in some implementations, the cleaning device 105 is designed as an inductively coupled plasma (ICP) cleaning device 405. As shown in FIG. Cleaning apparatus 405 includes plasma generator 480 that receives energy or power from power supply 485 . Plasma generator 480 is inside EUV chamber 225 , but power supply 485 can be located outside EUV chamber 225 . The plasma generator 480 is shaped similarly to the edge 211 of the reflective surface 210 of the collector mirror 215 . Therefore, since the edge 211 is circular, the plasma generator 480 is also circular.

[00079] Plasma generator 480 includes an electrical conductor 481 positioned adjacent to reflective surface 210 of collector mirror 215. Electrical conductor 481 may be electrically conductive. Conductor 481 is connected to power supply 485 . The conductor 481 is made of a conductive material such as metal. Conductor 481 is contained within tube 482 , and atmospheric pressure can be maintained between conductor 481 and tube 482 . Tube 482 can be made of a dielectric material such as porcelain, ceramic, mica, polyethylene, glass, or quartz. The conductor 481 can be hollow so that it can be water cooled (by running water inside the conductor 481). The path of the conductor 481 matches the shape of the edge 211 of the reflective surface 210 so that the energy generated from the plasma generator 480 interacts more efficiently with the reflective surface 210 and the native material 235 adjacent to the edge 211. enable The inner diameter of plasma generator 480 may be slightly larger than the diameter of edge 211 of reflective surface 210 so as not to interfere with the amount of EUV light 275 reflected from reflective surface 210 during operation of EUV light source 200 .

[00080] Any geometric configuration for the conductor 481 is possible. For example, conductor 481 may have an inner diameter about several centimeters (cm) smaller than edge 211 of reflective surface 210 . As shown, conductor 481 is circular. In other implementations where reflective surface 210 is rectangular, conductor 481 may be rectangular. Thus, conductor 481 may be triangular if reflective surface 210 is triangular, or conductor 481 may be linear if reflective surface 210 is in the form of a line or a straight line.

[00081] Referring to FIGS. 5A-5D, in some implementations, the cleaning device 105 is designed as an inductively coupled plasma (ICP) cleaning device 505. As shown in FIG. Similar to cleaning system 405 , cleaning system 505 includes plasma generator 580 that receives energy or power from power source 585 . Plasma generator 580 is internal to EUV chamber 225 , but power supply 585 can be external to EUV chamber 225 . The plasma generator 580 is shaped similarly to the edge 211 of the reflective surface 210 of the collector mirror 215 . Therefore, since the edge 211 is circular, the plasma generator 580 is also circular.

[00082] Plasma generator 580 includes an electrical conductor 581 positioned adjacent to reflective surface 210 of collector mirror 215. Electrical conductor 581 is electrically conductive. Conductor 581 is connected to power supply 585 . The conductor 581 is made of a conductive material such as metal. Conductor 581 is contained within tube 582 , but there is no gap between conductor 581 and tube 582 . Thus, tube 582 is in contact with conductor 581 and touches conductor 581 .

[00083] Tube 582 may be made of a dielectric material such as porcelain, ceramic, mica, polyethylene, glass, or quartz. The conductor 581 can be hollow so that it can be water cooled (by running water inside the conductor 581). The path of the conductor 581 matches the shape of the edge 211 of the reflective surface 210 so that the energy generated from the plasma generator 580 interacts more efficiently with the reflective surface 210 and the native material 235 adjacent to the edge 211. enable The inner diameter of plasma generator 580 may be slightly larger than the diameter of edge 211 of reflective surface 210 so as not to interfere with the amount of EUV light 275 reflected from reflective surface 210 during operation of EUV light source 200 .

[00084] In some implementations, instead of tube 582, a plurality of segmented beads 583, each composed of a dielectric material, are used, as shown in FIG. 5E. Beads 583 contact each other and contact conductor 581 . Furthermore, there is no air inside bead 583 . Therefore, even if the plasma generator 580 is damaged by an external impact, there is no possibility of air leakage.

[00085] One advantage of using a solid (filled) tube 582 or bead 583 is that between the conductor 581 and the dielectric material (tube 582 or bead 583) (as in plasma generator 480) The absence of air gaps. This gap is essentially an air (mostly oxygen) filled gap. For example, tube 482 is at risk of breaking due to external impact, and when this occurs, air in the region between tube 482 and conductor 481 is released into EUV chamber 125 . The design shown in Figures 5A-5E reduces this risk of exposing the EUV chamber 125 to air and oxygen.

[00086] An exemplary plasma generator 680 is shown in Figures 6A and 6B, and a close-up of a segment of the plasma generator 680 is shown in Figure 6C. Plasma generator 680 includes an electrical conductor 681 positioned adjacent reflective surface 210 of collector mirror 215 . Conductor 681 is connected to power source 685 and is made of a conductive material such as metal. The conductor 681 is contained within a sheath 682 composed of a plurality of bead-like solid segments 683 . Solid segments 683 are configured to intertwine to form a continuous shape around conductor 681 . As discussed above, there is no substantial air gap between sheath 682 and conductor 681 . Solid segment 683 of sheath 682 may be made of dielectric material such as porcelain, ceramic, mica, polyethylene, glass, or quartz.

[00087] Referring to Figure 7, a procedure 700 is performed for cleaning the surface 110 of the optics 115 in the EUV chamber 125, which is held at a sub-atmospheric pressure. Please refer to FIGS. 8A and 8B which schematically illustrate the steps of procedure 700 . As shown, a plasma state material (plasma material 130 ) is generated at a location adjacent to the optical surface 110 . This generation occurs within the EUV chamber 125 (705). As discussed above, plasma material 130 includes at least material ions, electrons, and free radicals. Generating plasma material 130 includes converting material already existing within EUV chamber 125 adjacent optical surface 110 from a first state (native material 135) to a plasma state (plasma material 130). (710). The plasma state of the material (plasma material 130) includes free radicals of the material. For example, if native material 135 includes molecular hydrogen, step 710 includes converting this molecular hydrogen to a plasma state that includes hydrogen free radicals H*. Material in the plasma state can be moved over the optical surface 110 to remove debris 107 from the optical surface 110 without removing the optics 115 from the EUV chamber 125 (715).

[00088] Plasma material 130 chemically reacts with debris 107 to form new chemicals 137, as shown in FIGS. 8A and 8B. New chemical 137 is in a gaseous state and is released from light surface 110 . For example, if native material 135 includes molecular hydrogen and debris 107 includes tin particles, step 615 includes producing tin hydride 237 as the new chemical by reaction of hydrogen free radicals H* with tin Sn. include.

[00089] Referring to FIG. 9, in some implementations where cleaning apparatus 105 is an ICP cleaning apparatus (such as cleaning apparatus 205, 405, or 505), procedure 910 for converting native material 135 to plasma material 130. is executed. In the ICP process, conductors 481, 581 (located outside the perimeter of light surface 110) are driven 911 with a time-varying current (from power sources 285, 485, 585). The time-varying current flow creates a time-varying magnetic field around the current within the EUV chamber 225 (912). The time-varying magnetic field generated around the current also induces an electric field or current at locations within the EUV chamber 225 adjacent to the optical surface 210 (913). The induced current (913) is large enough to generate plasma material 130 from the native material 135 within the EUV chamber 125 at a location adjacent to the reflective surface 210. FIG. Specifically, the changing or time-varying magnetic field (912) induces current in the regions around the conductors 481,581. In addition, this induced current produces its own magnetic field that opposes the time-varying magnetic field produced at 913, which produces its own current or induced electric field, which is the native magnetic field near the plasma generator. Flow to material 135 . The energy generated from this induced electric field transforms native material 135 into plasma material 130 (which induces plasma material 130 within EUV chamber 125).

[00090] Further, the magnitude of the induced electric field in the area around the conductors 481,581 is proportional to the magnitude of the conductors 481,581. Therefore, to increase the area or volume of plasma material 130, the size of conductors 481, 581 must be increased.

[00091] Procedures 700 and 910 are performed without the presence of oxygen as a catalyst or element for the reaction. The procedure 700 may also include removing chemicals emitted from the EUV chamber 125 using, for example, the exhaust device 295 .

[00092] Referring to FIGS. 10A and 10B, graphs 1000 and 1050 respectively determine the rate of removal of debris 107 from optical surface 110 using procedures 700 and 910 and ICP cleaning devices 205, 405, 505 (ICP). The results of tests performed to achieve this are presented in comparison to two conventional techniques (labeled HRG and MW in the graph). The horizontal axes of graphs 1000 and 1050 correspond to distance from ICP cleaning devices 205, 405, 505. FIG. The vertical axes of graphs 1000 and 1050 correspond to removal rate (arbitrary units). This data shows a significant improvement in removal rates using the ICP cleaners 205, 405, 505 compared to conventional techniques. For example, at a value of 5 arbitrary units from the ICP cleaners 205, 405, 505, the ICP cleaners 205, 405, 505 removed debris 107 at a rate 100 times faster than that of the HRG and MW techniques. Also, as the distance from the ICP cleaner 205, 405, 505 increases, the removal rate using the ICP cleaner 205, 405, 505 remains stable with no observable decrease. In some implementations, removal rates greater than 100 nm/min can be reached at 1-12 centimeters (cm) from the ICP cleaner 205, 405, 505. The outer diameter of the optical surface 210 of a typical collector mirror used in EUV light sources is about 60 cm.

[00093] The cleaning apparatus 105, 205, 405, 505 provides a much higher removal debris removal rate than conventional techniques, which is partly due to the free flow within the plasma material 130 at the optical surface 110, 210. This is because the density of radicals is significantly higher than in the prior art. This is also due, in part, to the fact that free radicals of the plasma material 130 are efficiently generated locally on the optical surface 110, 210 (rather than being transported from outside the EUV chamber 125) and the ICP cleaning equipment 205 , 405 , 505 designs are able to operate in a vacuum environment without oxygen, water, and other additional materials not natively present in the EUV chamber 125 .

[00094] Referring to FIG. 11, in some implementations the cleaning apparatus 105 (or 205, 405, 505) is implemented within an EUV light source 1100 that provides EUV light 1175 to a lithographic apparatus 1190. Lithographic apparatus 1190 is constructed to support an illumination system (illuminator) IL configured to condition a beam of radiation B (eg, EUV light 1175), and a patterning device (eg, mask or reticle) MA to precisely align the patterning device. a support structure (e.g. mask table) MT connected to a first positioner PM configured to position a substrate (e.g. a resist-coated wafer) W and configured to accurately position the substrate a substrate table (e.g. wafer table) WT connected to a second positioner PW connected to a target portion C (e.g. comprising one or more dies) of the substrate W, the pattern imparted to the radiation beam B by the patterning device MA; and a projection system (eg, a reflective projection system) PS configured to project onto.

[00095] The illumination system IL includes optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types, or any combination thereof, for directing, shaping, or controlling radiation. Various types of optical components can be included. The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus and conditions such as, for example, whether the patterning device is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure MT may for example be a frame or table which can be fixed or movable as required. The support structure MT may ensure that the patterning device is at a desired position, for example with respect to the projection system PS.

[00096] As used herein, the term "patterning device" refers to any device that can be used to impart a pattern to a cross-section of a beam of radiation so as to produce a pattern on a target portion of a substrate. should be interpreted broadly. The pattern imparted to the beam of radiation corresponds to specific functional layers of the device to be produced in the target portion, such as an integrated circuit. Patterning devices may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. be An example of a programmable mirror array uses a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern to the radiation beam reflected by the mirror matrix.

[00097] The projection system PS, as well as the illumination system IL, may include optical components such as refractive, reflective, magnetic, electromagnetic, electrostatic, etc., as appropriate to the exposure radiation used, or other factors such as the use of a vacuum. , or any combination thereof. It may be desirable to use a vacuum for EUV radiation because other gases absorb too much radiation. A vacuum environment can therefore be provided throughout the beam path using vacuum walls and vacuum pumps.

[00098] As indicated herein, the apparatus is of a reflective type (eg, using a reflective mask).

[00099] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more patterning device tables). In such "multi-stage" machines, additional tables may be used in parallel or preliminary steps may be performed on one or more tables while one or more other tables are being used for exposure. can be done.

Illuminator IL receives an extreme ultraviolet radiation beam (EUV light 1175 ) from EUV light source 1000 . Methods for generating EUV light include, but are not necessarily limited to, converting a material having at least one element with one or more emission lines in the EUV range, such as xenon, lithium, or tin, into a plasma state. include. One such method, often referred to as laser-produced plasma (“LPP”), involves irradiating a fuel such as, for example, droplets, streams, or clusters of material having the desired light-emitting element with a laser beam to generate the desired plasma. plasma can be generated. EUV light source 1100 can be designed like EUV light source 100 or 200 . As discussed above, the resulting plasma emits output radiation, such as EUV radiation, which is collected using optics 115, 215 (or radiation collectors).

[000101] The radiation beam B is incident on the patterning device (eg mask) MA, which is held on the support structure (eg mask table) MT, and is patterned by the patterning device. After being reflected from the patterning device (eg mask) MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position sensor PS2 (e.g. an interferometric device, a linear encoder or a capacitive sensor), the substrate table WT is precisely positioned, e.g. to position various target portions C in the path of the radiation beam B. can move. Similarly, a first positioner PM and another position sensor PS1 may be used to accurately position the patterning device (eg mask) MA with respect to the path of the radiation beam B. FIG. Patterning device (eg mask) MA and substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2.

[000102] The illustrated lithographic apparatus can be used in at least one of the following modes.
1. In step mode, the support structure (e.g. mask table) MT and substrate table WT are kept essentially stationary while the entire pattern imparted to the radiation beam is projected onto the target portion C in one go (i.e. single static exposure). The substrate table WT is then moved in the X and/or Y direction so that a different target portion C can be exposed.
2. In scan mode, the support structure (eg mask table) MT and substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (ie a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (eg mask table) MT may be determined by the magnification (demagnification) and image reversal properties of the projection system PS.
3. In another mode, the support structure (e.g. mask table) MT holds the programmable patterning device and is kept essentially stationary and the substrate table WT is moved or scanned while the pattern imparted to the radiation beam is directed onto the target portion. Project to C. In this mode, a pulsed radiation source is typically used to update the programmable patterning device as needed each time the substrate table WT is moved, or between successive radiation pulses during a scan. This mode of operation is readily available for maskless lithography using programmable patterning devices such as programmable mirror arrays of the type referred to above.

[000103] Combinations and/or variations of the above-described modes of use, or entirely different modes of use may also be utilized.

[000104] Figure 12 shows in more detail an implementation of a lithographic apparatus 1290 that includes an EUV light source 1200, an illumination system IL, and a projection system PS. The EUV light source 1200 is constructed and arranged as discussed above when describing the EUV light sources 100,200.

[000105] Systems IL and PS are similarly housed within their own vacuum environment. The intermediate focus (IF) of the EUV light source 1200 is configured so that it is located at or near the aperture of the closed structure. The virtual source point IF is an image of a radiation emitting plasma (eg EUV light 165).

[000106] From the aperture at intermediate focus IF, the radiation beam traverses illumination system IL, which in this example includes facetted field mirror device 1222 and facetted pupil mirror device 1224. FIG. These devices form so-called "fly's eye" illuminators. It is arranged to provide the desired angular distribution of the radiation beam 1221 at the patterning device MA and the desired radiation intensity uniformity at the patterning device MA (indicated by reference numeral 1260). A patterned beam 1226 is formed when the beam 1221 is reflected off the patterning device MA, which is held by the support structure (mask table) MT. This patterned beam 1226 is imaged by the projection system PS via reflective elements 1228, 1230 onto the substrate W held by the substrate table WT. To expose a target portion C on the substrate W, the substrate table WT and the patterning device table MT move in synchronism to scan the pattern on the patterning device MA through the illumination slit while generating pulses of radiation.

[000107] Each system IL and PS is located within its own vacuum or near-vacuum environment defined by a closed structure similar to the EUV chamber 125 . More elements than shown may generally be present in illumination system IL and projection system PS. Additionally, there may be more mirrors than shown. For example, there may be from 1 to 6 additional reflective elements beyond those shown in FIG. 12 in illumination system IL and/or projection system PS.

[000108] Referring again to FIG. can include In operation, the amplified light beam 160 is delivered synchronously with the operation of the droplet generator to deliver a pulse of radiation for transforming each droplet (each target 150 ) into a light emitting plasma 170 . The frequency of droplet ejection may be several kilohertz, for example 50 kHz.

[000109] In some implementations, the energy from amplified light beam 160 is delivered in at least two pulses. That is, a pre-pulse of limited energy is delivered to the droplets prior to reaching the interaction region 155 to vaporize the fuel material into a small cloud, and then a main pulse of energy is delivered to generate the light emitting plasma 170. It is sent out to the cloud of interaction areas 155 . A trap (which may be, for example, a receptacle) is provided on the opposite side of the EUV chamber 125 to capture fuel (ie, target 150) that for some reason does not turn into plasma.

[000110] The droplet generator in target delivery system 140 comprises a reservoir containing a fuel liquid (eg, molten tin), a filter, and a nozzle. The nozzle is configured to emit droplets of fuel liquid toward interaction region 155 . A combination of pressure in the reservoir and vibration applied to the nozzle by a piezo actuator (not shown) can cause a droplet of fuel liquid to be expelled from the nozzle.

[000111] Other aspects of the invention are described in the following numbered clauses.

1. 1. A method of cleaning surfaces of optics in a chamber of an extreme ultraviolet (EUV) light source, the chamber being held at a pressure below atmospheric pressure, the method comprising:
Generating material in a plasma state at a location in the chamber adjacent to the optical surface, generating the native material already present in the vacuum chamber adjacent to the optical surface from a first state into the plasma. including converting to a state,
The plasma state of the material contains free radicals of the material,
The method wherein generating the material in the plasma state includes moving the material in the plasma state over the optical surface to enable removal of debris from the optical surface without removing the optics from the EUV light source.
2. 2. The method of clause 1, wherein generating the plasma state material includes electromagnetically inducing a current at a location in the chamber adjacent to the optical surface.
3. 3. The method of clause 2, wherein inducing a current at a location adjacent to the optical surface within the chamber includes generating a time-varying magnetic field near an optical system within the chamber.
4. 4. The method of clause 3, wherein generating a time-varying magnetic field within the chamber comprises passing a time-varying current through an electrical conductor positioned outside the perimeter of the optical surface.
5. 2. The method of clause 1, wherein moving the material in the plasma state across the optical surface to enable removal of debris from the optical surface is performed in the absence of oxygen.
6. 2. The method of clause 1, wherein the material in the plasma state comprises at least hydrogen ions, electrons and free radicals.
7. 2. The method of clause 1, wherein removing debris from the optical surface comprises chemically reacting free radicals of the material with the debris on the optical surface to form chemicals that are released from the optical surface.
8. 8. The method of clause 7, further comprising removing released chemicals from the EUV chamber.
9. 8. The method of clause 7, wherein the free radicals are hydrogen free radicals and the debris on the photosurface comprises tin, such that the chemical released from the photosurface comprises tin hydride.
10. 2. The method of clause 1, wherein removing debris from the optical surface comprises etching debris from the optical surface at a rate of at least 1 nanometer/minute across the optical surface.
11. An extreme ultraviolet (EUV) light source,
an EUV chamber maintained at a pressure below atmospheric pressure;
A target delivery system for directing a target toward an interaction region within a vacuum chamber, the interaction region receiving an amplified light beam, the target comprising a material that emits extreme ultraviolet light when converted to plasma. a target delivery system, including
a light collector including a surface that interacts with at least a portion of the emitted extreme ultraviolet light;
A cleaning apparatus adjacent to a light collector surface and configured to remove debris from the light collector surface without removing the collector from the EUV chamber, the cleaning apparatus comprising a plasma generator in the EUV chamber adjacent to the light collector surface, the plasma generator generates plasma material in a plasma state adjacent to the light collector surface from native material already existing in a first state in the EUV chamber adjacent to the light collector surface, the plasma material a cleaning device comprising free radicals that chemically react with debris on the surface;
A system with
12. 12. The system of clause 11, wherein the light collector surface is a reflective surface and the interaction of the light collector surface with the emitted extreme ultraviolet light includes reflection of the emitted extreme ultraviolet light from the light collector surface.
13. The plasma generator includes an electrical conductor positioned adjacent to the light collector surface, the electrical conductor connected to a power source, the power source supplying a time-varying current through the electrical conductor to generate a current when adjacent the light collector surface. generating a changing magnetic field and inducing a current at a location adjacent to the light collector surface;
12. Clause 11, wherein the induced current is sufficiently large to generate plasma state material at a location adjacent to the light collector surface from native material already present in the EUV chamber in a first state. system.
14. 14. The system of clause 13, wherein the electrical conductor is shaped to match the shape of the light collector surface.
15. 14. The system of clause 13, wherein the plasma generator includes a dielectric material that at least partially surrounds the electrical conductor.
16. 16. The system of Clause 15, wherein the dielectric material comprises a tube surrounding at least a portion of the conductor.
17. 17. The system of clause 16, wherein the tube contacts a portion of the conductor.
18. 15. The system of clause 14, wherein the electrical conductor is shaped to match the shape of a rim at the edge of the light collector surface.
19. 14. The system of clause 13, wherein the light collector surface is elliptical in shape and the conductor comprises a circle having a diameter greater than the circumference of the light collector surface.
20. 12. The system of clause 11, wherein the native material already present in the chamber in the first state comprises hydrogen and the material in the plasma state comprises at least ions, electrons and free radicals of hydrogen.
21. 12. The system of clause 11, wherein a chemical reaction between free radicals and debris on the light collector surface forms chemicals that are released from the light collector surface.
22. 22. The system of Clause 21, further comprising a removal device configured to remove chemicals released from the EUV chamber.
23. 22. The system of clause 21, wherein the free radicals are hydrogen free radicals and the debris on the light collector surface comprises tin, such that the chemicals released from the light collector surface comprise tin hydride.
24. 22. The system of clause 21, wherein debris from the light collector surface is etched away by free radicals at a rate of at least 1 nanometer/minute across the light collector surface.
25. 12. The system of clause 11, wherein the cleaning device includes an inductively coupled plasma source.
26. 1. A method of cleaning surfaces of optics in a chamber of an extreme ultraviolet (EUV) light source, the chamber being held at a pressure below atmospheric pressure, the method comprising:
Generating material in a plasma state at a location in the chamber adjacent to the optical surface, the generating comprising:
converting a material in the vacuum chamber from a first state to a plasma state by electromagnetically inducing a current at a location adjacent to the optical surface in the chamber;
The plasma state of the material contains free radicals of the material,
The method wherein generating the material in the plasma state includes moving the material in the plasma state over the optical surface to enable removal of debris from the optical surface without removing the optics from the EUV light source.
27. 27. The method of clause 26, wherein the material is in the first state and is adjacent to the optical surface before being transformed.
28. 27. The method of clause 26, wherein inducing a current at a location adjacent to the optical surface within the chamber includes generating a time-varying magnetic field near an optical system within the chamber.
29. 29. The method of clause 28, wherein generating a time-varying magnetic field within the chamber comprises passing a time-varying current through an electrical conductor positioned outside the perimeter of the optical surface.
30. 27. The method of clause 26, wherein moving the material in the plasma state across the optical surface to enable removal of debris from the optical surface is performed in the absence of oxygen.
31. 27. The method of clause 26, wherein the material in the plasma state comprises at least hydrogen ions, electrons and free radicals.
32. Removing debris from the optical surface includes chemically reacting free radicals of the material with debris on the optical surface to form chemicals that are released from the optical surface, the method further releasing from the EUV chamber. 27. The method of Clause 26, comprising removing the chemical that has been removed.
33. 33. The method of clause 32, wherein the free radicals are hydrogen free radicals and the debris on the photosurface comprises tin, such that the chemical released from the photosurface comprises tin hydride.
34. 27. The method of clause 26, wherein the material in the vacuum chamber is native and present in the vacuum chamber.

[000112] Other implementations are within the scope of the following claims.

Claims (34)

1. A method of cleaning optical surfaces within a chamber of an extreme ultraviolet (EUV) light source, said chamber being held at a pressure below atmospheric pressure, said method comprising:
generating material in a plasma state at a location within the chamber adjacent to the optical surface, said generating first removing native material already present within the vacuum chamber adjacent to the optical surface; converting from a state of 1 to a plasma state;
said plasma state of said material comprises free radicals of said material;
Generating the material in the plasma state moves the material in the plasma state over the light surface to enable removal of debris from the light surface without removing the optics from the EUV light source. A method comprising: 2. The method of claim 1, wherein generating the material in the plasma state comprises electromagnetically inducing a current at the location adjacent the optical surface within the chamber. 3. The method of claim 2, wherein inducing the current at the location adjacent the optical surface within the chamber comprises generating a time-varying magnetic field near the optical system within the chamber. 4. The method of claim 3, wherein generating the time-varying magnetic field within the chamber comprises passing a time-varying current through an electrical conductor positioned outside the perimeter of the light surface. 2. The method of claim 1, wherein moving the material in the plasma state across the optical surface to enable removal of debris from the optical surface is performed in the absence of oxygen. 2. The method of claim 1, wherein the material in the plasma state comprises at least hydrogen ions, electrons and free radicals. 4. The method of claim 1, wherein removing debris from the optical surface comprises chemically reacting free radicals of the material with the debris on the optical surface to form chemicals that are released from the optical surface. 1. The method according to 1. 8. The method of Claim 7, further comprising removing the released chemicals from the EUV chamber. 8. The method of claim 7, wherein the free radicals are hydrogen free radicals and the debris on the photosurface comprises tin, such that the chemicals released from the photosurface comprise tin hydride. 2. The method of claim 1, wherein removing the debris from the optical surface comprises etching the debris from the optical surface at a rate of at least 1 nanometer/minute across the optical surface. An extreme ultraviolet (EUV) light source,
an EUV chamber maintained at a pressure below atmospheric pressure;
A target delivery system for directing a target towards an interaction region within said vacuum chamber, said interaction region receiving an amplified light beam, said target emitting extreme ultraviolet light when converted to plasma. a target delivery system comprising a substance that
a light collector comprising a surface that interacts with at least a portion of said emitted extreme ultraviolet light;
A cleaning apparatus adjacent to the light collector surface and configured to remove debris from the light collector surface without removing the collector from the EUV chamber, the plasma in the EUV chamber adjacent to the light collector surface. a generator, said plasma generator generating plasma in a plasma state adjacent said light collector surface from a native material already existing in said EUV chamber in a first state adjacent said light collector surface; a cleaning apparatus for generating a material, the plasma material comprising free radicals that chemically react with the debris on the light collector surface;
A system with 3. wherein said surface of said light collector is a reflective surface and said interaction of said light collector surface with said emitted extreme ultraviolet light comprises reflection of said emitted extreme ultraviolet light from said light collector surface. Item 12. The system according to Item 11. The plasma generator includes an electrical conductor positioned adjacent to the light collector surface, the electrical conductor connected to a power supply, the power supply supplying a time-varying current through the electrical conductor to cause the light to generating a time-varying magnetic field adjacent to a collector surface and inducing a current at the location adjacent to the light collector surface;
The induced current is sufficiently large to generate the material in the plasma state at the location adjacent to the light collector surface from native material already present in the first state within the EUV chamber. 12. The system of claim 11, wherein: 14. The system of claim 13, wherein said electrical conductor is shaped to match the shape of said light collector surface. 14. The system of claim 13, wherein said plasma generator includes a dielectric material at least partially surrounding said electrical conductor. 16. The system of claim 15, wherein said dielectric material comprises a tube surrounding at least a portion of said electrical conductor. 17. The system of claim 16, wherein said tube contacts a portion of said conductor. 15. The system of claim 14, wherein said conductor is shaped to match the shape of a rim at the edge of said light collector surface. 14. The system of claim 13, wherein the light collector surface is elliptical in shape and the conductor comprises a circle having a diameter greater than the circumference of the light collector surface. 12. The method of claim 11, wherein the native material already present in the chamber in the first state comprises hydrogen and the material in the plasma state comprises at least hydrogen ions, electrons and free radicals. system. 12. The system of claim 11, wherein the chemical reaction between the free radicals and the debris on the light collector surface forms chemicals released from the light collector surface. 22. The system of Claim 21, further comprising a removal device configured to remove said released chemicals from said EUV chamber. 22. The method of claim 21, wherein the free radicals are hydrogen free radicals and the debris on the light collector surface comprises tin, such that the chemicals released from the light collector surface comprise tin hydride. system. 22. The system of claim 21, wherein the debris from the light collector surface is etched away by the free radicals at a rate of at least 1 nanometer/minute across the light collector surface. 12. The system of claim 11, wherein said cleaning device comprises an inductively coupled plasma source. 1. A method of cleaning optical surfaces within a chamber of an extreme ultraviolet (EUV) light source, said chamber being held at a pressure below atmospheric pressure, said method comprising:
generating material in a plasma state at a location in the chamber adjacent to the optical surface, the generating comprising:
converting a material in the vacuum chamber from a first state to the plasma state by electromagnetically inducing a current at the location adjacent the optical surface in the chamber;
said plasma state of said material comprises free radicals of said material;
Generating the material in the plasma state moves the material in the plasma state over the light surface to enable removal of debris from the light surface without removing the optics from the EUV light source. A method comprising: 27. The method of claim 26, wherein the material is adjacent to the optical surface before being transformed in the first state. 27. The method of claim 26, wherein inducing the current at the location adjacent the optical surface within the chamber comprises generating a time-varying magnetic field near the optical system within the chamber. 29. The method of Claim 28, wherein generating the time-varying magnetic field within the chamber comprises passing a time-varying current through an electrical conductor positioned outside the perimeter of the light surface. 27. The method of claim 26, wherein moving the material in the plasma state across the optical surface to enable removal of debris from the optical surface is performed in the absence of oxygen. 27. The method of claim 26, wherein the material in the plasma state comprises at least hydrogen ions, electrons and free radicals. removing debris from the optical surface comprises chemically reacting free radicals of the material with the debris on the optical surface to form chemicals that are released from the optical surface; 27. The method of claim 26, further comprising removing the released chemicals from the EUV chamber. 33. The method of claim 32, wherein the free radicals are hydrogen free radicals and the debris on the photosurface comprises tin, such that the chemicals released from the photosurface comprise tin hydride. 27. The method of claim 26, wherein the material within the vacuum chamber is native within and present within the vacuum chamber.

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